US Patent 7815089 Fastener gun

A fastener gun includes a housing having a plunger and a power spring for driving a fastener into a workpiece, and a trigger arm pivotally attached to the housing at a trigger pivot. One end of the trigger arm lifts the plunger to bias the power spring when the trigger arm pivots in a first direction toward the housing. A member contacting the trigger arm is provided that moves away from the trigger pivot as the handle moves toward the housing, so that force is applied at different locations on the trigger arm when the handle is squeezed, increasing the mechanical advantage of using the fastener gun.